Collaborative Research: Genetic diversity, resistance genes, and negative density dependence in tropical tree seedling dynamics

热带森林以其高度的多样性以及大量的稀有物种而闻名。最近的研究发现，与普通树种相比，稀有热带树种更容易受到专门针对单一寄主物种的病原体的影响，然后这些病原体会通过该单一寄主的密集苗木迅速传播。这项研究将检验这一新的假说，即稀有物种受到寄主特有病原体的影响更大，因为它们在种群水平上的抗性基因多样性较低，因此它们的所有幼苗都将对同一套病原体敏感，从而促进病原体的快速传播并增加死亡率。这一假设将通过实验温室和田间研究来验证，结合遗传分析，将量化巴拿马巴罗科罗拉多岛低地热带森林中稀有和常见树种的抗性基因多样性。计算机模拟也将被用来检验所测量的抗性基因多样性的差异是否会影响感染水平、死亡率和当地树木物种的丰富度。这项研究的结果将提高对植物-病原菌相互作用的理解，具有潜在的农业和园艺应用(例如，提高作物的病原菌抗性)。通过为学生和教师举办的暑期讲习班，将向更广泛的受众提供尖端基因技术的动手培训。这项研究将首次从树木群落获得大型转录组数据集，并将提供基因序列数据，为今后研究热带森林的遗传多样性提供信息。研究抗性基因多样性对森林动态的影响，将弥合分子进化研究与这种多样性在自然界中如何发挥作用之间的差距。分子进化研究表明，在许多基因座上正在进行多个抗性基因的选择。此外，这项研究可能会为热带植物多样性的相互竞争的理论架起桥梁，为为什么稀有树种更强烈地受到物种特有的敌人的控制提供了遗传解释，同时支持将扩散限制作为决定哪些物种在当地占主导地位的特征。最终，这项研究应该阐明，当地的稀缺性是否限制了当地的遗传多样性，这反过来又加强了当地的稀缺性，只有通过远距离花粉或种子流动招募新的等位基因才能逃脱这个循环。证明种群的生态和遗传特征之间的这种耦合将为进化和生态学的理论进步带来新的视角和途径。该项目将为本科生和研究生以及博士后研究员提供研究经验。

Tropical forests are famous for their high diversity, as well as the large number of rare species they harbor. Recent studies have found that, compared to common species, rare tropical tree species suffer more from pathogens that are specialized to a single host species that then spread rapidly through dense patches of seedlings of that single host. This research will test the novel hypothesis that rare species are more strongly impacted by host-specific pathogens because they have lower diversity of resistance genes at the population level, such that all their seedlings will be susceptible to the same suite of pathogens, promoting rapid pathogen spread and increasing mortality rates. This hypothesis will be tested using experimental greenhouse and field studies, combined with genetic analyses that will quantify the diversity of resistance genes for rare and common tree species in lowland tropical forest on Barro Colorado Island, Panama. Computer simulations will also be used to examine whether the measured differences in resistance gene diversity would impact infection levels, mortality rates and local abundance of tree species. Results of this study will improve understanding of plant-pathogen interactions, with potential applications for agriculture and horticulture (e.g. increasing pathogen resistance in crops). Hands-on training in cutting-edge genetic techniques would be provided to a wider audience through a summer workshop for students and faculty.This study will be the first to obtain large transcriptome datasets from a tree community and will provide gene sequence data that will be informative for future studies of genetic diversity in tropical forests. Examination of the effects of resistance gene diversity on forest dynamics will bridge the gap between molecular evolution studies that indicate ongoing selection for multiple resistance genes at many loci, and how this diversity functions in nature. Furthermore, this study is likely to bridge competing theories for tropical plant diversity by providing a genetic explanation for why rare tree species are more strongly controlled by their species-specific enemies, while simultaneously supporting dispersal limitation as a feature determining which species are locally dominant. Ultimately, the study should elucidate whether local rarity restricts local genetic diversity, which in turn reinforces local rarity, a cycle that can be escaped only by recruitment of new alleles via long-distance pollen or seed movement. Demonstrating such a coupling between the ecological and genetic features of populations would bring new perspectives and avenues for theoretical advances in evolution and ecology. The project will provide research experiences for undergraduate and graduate students, as well as a postdoctoral researcher.